The invention pertains to a process for making cellulose extrudates from an optically anisotropic solution containing 94-100 wt. % of the following constituents:
cellulose, PA1 phosphoric acid and/or its anhydrides, and PA1 water, PA1 1 reducing the cellulose in size, PA1 2 mixing the cellulose and the phosphoric acid-containing solvent, and PA1 3 dissolving the cellulose in the solvent. PA1 C.sub.w =the weighed out quantity of coagulated and washed cellulose.
by extruding the solution and then coagulating the formed extrudates.
Such a process is disclosed in our co-pending patent application based on the Netherlands patent application NL 9401351.
It was found that fibres obtained by extruding and coagulating the solution mentioned in the opening paragraph are particularly susceptible to heat treatment. For instance, it has been found that a heat treatment of 5 minutes at 175.degree. C. can result in the breaking force of the fibres being reduced by about 80% as compared with the original breaking tenacity.